Four stroke high r.p.m. internal combustion engine for racing purposes



C3. FUNICIELLQ FOUR STROKE HIGH R.P.M.

Aug. 8, 1%"? 3,334,313 INTERNAL COMBUSTION ENGINE FOR RACING PURPOSES 2Sheets-Sheet 1 Filed. May 14,-1965.

INVENTOR- J/MZ/D FU/VIUE Jam L; M6,,

ataya FUNHCIELLO wmm PM. INTERNAL COMBUSTION ENGINE FOR RACING PURPOSESAug. 8, 1967 Q FOUR STROKE HIGH R.

2 Sheets-Sheet 2 Filed May 14, 1965 FME PME

PME 00 a s I (X 1 5 INVENTOR- oRH 11c FwpIC/ELLO BY 1 n 3 3 UnitedStates Patent 11 Claims. (Cl. 123-75) This invention relates to a fourstroke, high r.p.m. internal combustion engine, for racing purposes. Inmore detail, the invention firstly concerns a lift diagram of inlet andexhaust valves for such engines.

As well known from the literature, the following requirements are to bemet for attaining a high specific horsepower: a decrease in the volumeand extension of the combustion chamber, thus increasing the so calledcompactness thereof (defined as the ratio of chamber volume to the areaof surface by which the chamber is defined), an increase in the sizes ofinlet and exhaust valves; attainment of a good turbulene in thecombustion chamber.

In four stroke engines for racing purposes, to which the invention isparticularly related, the above requirements are partly met by havingrecourse to very small piston displacements, i.e. by subdividing thetotal swept volume into a large number of cylinders. However, suchsolution results in a number of drawbacks, as: a lower mechanicalefficiency, a lower thermal efiiciency, a greater weight, a greaterbulk, increased likelihood of troubles and misadjustments, and finally ahigher cost.

The ideal solution would be one providing a highly compact combustionchamber, a large valve size and a good turbulence, by simple andreliable means, without having recourse to a large number of cylindersresulting in excessive splitting of total swept volume.

The main purpose of this invention consists in the provision of a designwhich provides high specific horsepowers by improving the combustionchamber compactness, the turbulence and the size of valve ports, Withouthaving recourse to an excessive splitting-up of the total swept volume,by merely acting on the lift diagram of inlet and exhaust valves, incombination with a very small value of the strokezbore ratio, and with aparticular shape of piston dome.

In more detail, the invention proposes to have one or more overheadvalves closed or nearly closed at to dead center, in order to allow thepiston dome to contact or nearly contact the valve heads at top deadcenter. Thus, the space that is taken-up by the burning mixture is muchsmaller than the conventional hemispheric one, which, in the high r.p.m.versions for racing purposes, essentially consists in the space that isleftover, at the top dead center, between the valve and piston dome, andthat is necessarily takenup, at overlapped opening of valves at top deadcenter, by the valves, which at this moment are wide open in aconventional high rpm. engine. That is, while in the latter engine theexpanding products of the combustion are compressed essentially in thespace which is taken-up by the valves at the top dead center (i.e. thatof exhaust stroke end), thereby providing the overlap, in the novelengine of the present invention, the gases are squished from such space(related to one or more valves), and forced into a space that is muchsmaller than the heads of these valves.

Thus, the magnitude of the actual combustion chamber in the novel engineof the present invention is not depend ent on valve size, wherebyrecourse can be made to very large valves, fitted in ports that areunusually large with respect to valve stroke, thus obtaining also thewell known 3,334,618 Patented Aug. 8, 1967 advantages associated withthe very short strokes. The

valves that in the novel engine are closed (or nearly closed) at topdead center and will thereby take-up a portion of opening diagramsmaller (by approximately 30%) than in a conventional diagram. However,this reduction is more than balanced by their much greater valve size orgeometric section (that may be, in total, double the conventional one).

Moreover, according to a further proposal of the invention, theoverlapped intake and exahust openings at top dead center (advance ofthe inlet opening and scavenging of combustion chamber due to action ofexhaust gases) is performed by having the valves, that are closedprecisely at the instant of top dead center, again openedbefore or aftertop dead center, according to the function (inlet or exhaust) of samevalves. Otherwise stated, the inlet valve is partially open directlybefore top outer dead center, and closed again when same center isattained, Whereafter it is wholly opened for the entire time of inletstroke. Similarly, the exhaust valve is closed at the same dead center,whereafter it is partly opened, and is definitely closed as soon as thepressure in the cylinder is reduced to a value lower than that in theexhaust manifold. In other words, it may be conceived that a maximum isattained by the opening diagram of inlet valve, when the latter valve isadditionally opened, while a minimum is attained in the same diagram atthe top dead center (which minimum may correspond, e.g., to a zero valueof the opening of the valve), whereafter a new maximum distinctly higherthan the preceding one is attained after top dead center. By such formof the additional opening diagram, the maximum opening is attainedduring the additional opening. However, it is to be understood that anyother form of additional opening diagram will fall in the range of theinvention, on condition that the noun erical requirements, as statedlater on, are met. Thus, e.g., the value of maximum of the extra-openingmay be equal to the minimum which is attained at the top dead center.

As stated previously, the closing at top dead center may also not becomplete, and in such a position, the valve head may be drawn away fromits seat by a maximum distance on the order of a few millimeters.

In addition to such additional openings, the overlap may be performedeven by other valves, facing the compact combustion chamber, and thushaving a conventional opening diagram. Obviously, recourse may be madeto a combination of additional opening and conventional valves, as wellas to either solution, according to particular operational requirements.

To sum up; the invention proposes to have the well known squishphenomenon realized on one or more valves, by having the opening thereofdrastically restricted at the top dead center, without howeverrestricting the opening of said valves before, and after same top deadcenter; and by the use of further valves, in combination with thesevalves, but having a conventional opening diagram.

The squish was heretofore present either on stationary sections of head,or even on the valves, being permitted by the fact that the engine, notof the high r.p.rn. type, has a small overlap, and thus a small valveopening at top dead center. Conversely, the novel motor entails asubstantial change in the distribution diagram, since it has a largeoverlap, and simultaneously one or more valves closed, or nearly closedat top dead center, as a result of the above-described additionalopenings, and by the presence of further valves, having conventionalopening diagrams, i.e. diagrams different from those of valves that areclosed at top dead center.

The basic features of the engine of the invention are very differentfrom those of conventional engines, namely: a very compact combustionchamber, very large valves, a piston stroke which is very small withrespect to cylinder bore, so much so that the stroke/bore ratio which isthe most suitable for the engine would be impracticable for aconventional engine, and the shapes and combinations of different valveopening diagrams, which can be summarized as follows:

The condition:

K /sD is met by the distance between the piston dome, and the side of atleast one overhead valve facing the same, on attaining top dead centerat the end of the exhaust stroke (K said distance; D=Max. lift ofrelated valve from its seat). H

An additional overlap opening is provided, before top dead center of theexhaust stroke, by at least one intake valve, besides the normal openingin the course of inlet stroke, this additional opening being maintainedthrough an angular travel a of crankshaft meeting the followingcondition:

oc 35 deg.

An additional overlap opening is provided, after top dead center of theexhaust stroke, by at least one exhaust valve, besides the normalopening in the course of exhaust stroke, this additional opening beingmaintained through .an angular travel of crankshaft, meeting thefollowing condition:

fl 35 deg.

As a result, high specific horsepowers are attained without thenecessity of having the total swept volume split into a large number ofcylinders, with all related dis advantages, while obviously even higherhorsepowers are attained when the invention is carried into practicealong with a high splitting-up of swept volume.

The invention will be better appreciated from a consideration of thefollowing detailed description taken with the accompanying drawings,both description and drawings being given as a non-restrictive exampleonly. In the drawings:

FIG. 1 is a diagrammatic axial section of a cylinder with a pistontherein, and provided with two inlet valves and two exhaust valves-thestructure being shown in the position of combustion at top dead center.

FIG. 2 is a section taken on the line 11-11 of FIG. 1.

FIG. 3 is a section taken on the line IIIIII of FIG. 1.

FIG. 4 shows a possible operating diagram for the valves of the engineas shown in the preceding figures, the valve lifts being plotted on theordinate, while the angular travel of the crankshaft is plotted on theabscissa.

Referring now to FIGS. 1 to 4 inclusive, 1 is a cylinder, having fourvalves 2, 2a and 4, 4a at its head. The valves 2 and 2a are locatedoff-center, with respect to the longitudinal axis of the piston, and arerespectively designed to operate as an inlet valve and as an exhaustvalve. 3 is the inlet pipe, while 3a is the exhaust pipe. The other twovalves are: an inlet valve 4, and an exhaust valve 4a, which lead to anoffset small combustion chamber 5, wherein the spark plug 6 is located.Said combustion chamber 5 is defined in part by the cylinder head, andin part by a cavity in the dome 9 of piston 8.

The pipes 7 and 7a, that are controlled by the valves 4 and 411,respectively lead into the tubes 3 and 3a (see FIG. 2).

As it can be seen from the figures, the shape of piston dome is partlymatched with that of cylinder head, in the section where the valves 2and 2a are located. In that section, the piston upper side cooperateswith the cylinder head inside, and with the valves 2 and 2a to cause,toward the end of the compression stroke, an expulsion of gaseous masstoward the combustion chamber 5 where, as a consequence thereof, ahighly efficient turbulence is induced, thus providing a thorough mixingand a quick combustion. Otherwise stated, the so called squish-- 4 wellknown to the persons skilled in the artis obtained.

The combustion chamber is thus unusually compact. It is faced by bothvalves 4 and 4a, and by the ignition plug 6.

The sizes of said valves 4 and 4a are smaller than those of both othervalves 2 and 2a that are contacted or almost contacted by the piston,with consequent squish and swirl, as indicated by the arrow A.

The axes of both smaller valves 4 and 4a converge at an angle wider thanthat of larger valves, whereby a common camshaft (not shown) can be usedfor all valves.

Thus, the engine is characterized by an off-center combustion chamber,by the presence of four valves (i.e. two inlet valves and two exhaustvalves), two of the valves being situated at the top of the combustionchamber, while the other two valves are contacted by the piston dome 9when the top dead center is attained.

According to the invention, a typical and distinctive operating diagramis established for the valves. Such diagram differs from that ofconventional valves, due to following basic features:

The additional openings. The material difference between the diagrams ofvalves 2 and 2a, and the diagrams of valves 4 and 4a.

The coexistence of a marked overlap, with some of the valves closed (ornearly closed) at top dead center.

For a better understanding of the difference in the valve lift diagrams,reference will be made to FIG. 4, which shows a diagram that representsthe motion of all four valves (and namely the lifting of the valves fromtheir seats, as a function of the angular travel of the crankshaft,which is plotted on the abscissa). In FIG. 4, the top dead centers andthe bottom dead centers of the piston are respectively indicated by thereference letters PME and PMI, while the solid line P and the solid lineQ respectively indicate the motions of valves 4 and 4a, i.e. of thevalves facing the combustion chamber 5, and the dash lines R, Srespectively indicate the motion of valves 2 and 2a.

As it can be readily seen from the above diagram, the valves 2 and 2aare wholly closed at each top dead center, and an additional opening isimparted thereto, while the usual motion is followed by the valves 4 and4a. According to the invention, the lift of valves 2 and 2a is nil atthe top dead center by which the condition K /eD is met (being K=O,while D is the max. lift of valve that is closed at the top deadcenter). The condition oc 35 is met by the advance at in the opening ofinlet valves (in FIG. 4 Ot= deg), and similarly the condition i3 35 deg.is met by the closing delay [3 of the exhaust (in FIG. 4 5:60 deg.

The operation i as follows: the cylinder head is contacted or almostcontacted by a large portion of dome of piston 8, when this latter is attop dead center, whereby the gases are expelled, while swirling, intothe particularly compact combustion chamber 5, due to the fact that thevalves 2 and 2a are closed under such conditions, the overlap beingobtained with the valves 4 and 4a, while an overlap is obtained by thevalves 2 and 2a due to additional openings.

To prevent the gases which, on attaining the overlap region, are forcedby the piston dome & toward the chamber 5 from entering directly intothe open port of inlet valve 4, the plane of such valve is set back inrespect of that of inlet valve 2, whereby the gas streams that areforced out of the zone wherein the piston dome 9 comes into contact withthe cylinder head are not directed toward the valve port, which wouldprevent an efficient induction. The same effect could however beattained by having a ridge or step formed on the cylinder head, or onthe piston dome.

According to another embodiment form (not shown) both piston andcylinder can be formed as shown in the FIGS. 1 to 3, except that the twovalves 4 and 41:, facing the combustion chamber 5, are left out; i.e.the cylinder 3 is fitted with the inlet valve 2 and exhaust valve 21,designed to be contacted by the dome 9 of piston 8. In this embodiment,additional openings will necessarily be provided by the valves 2 and 2a(which however would be unnecessary, as previously stated, when theoverlap is provided by other valves, with which the engine is fitted, inaddition to valves 2 and 2a).

The operation is obvious, namely: about the end of exhaust stroke when,as an effect of the exhaust flow of the column of burnt gases, a vacuumis formed in the cylinder 1 (in the example, at ab. 300 deg), the inletvalve 2 is opened, and is however closed again, together with theexhause valve, when the top dead center is attained by the piston. Then,as soon as the intake stroke is started by the piston 8, which movesaway from the outer dead center, both valves are again opened.

However, while the inlet valve is opened up to its maximum lift, theexhaust valve is closed as soon as the vacuum, which is formed in thecylinder, would cause a flow of gas back from the exhaust. In thespecific example, this occurs at approximately 420 deg.

As already stated, both valves 2 and 2a may also not be wholly closed atthe top dead center, i.e. the invention covers also a solution whereinthe piston dome 9 is ridged all around its contour as shown by the dashline 82. Thus, in the latter case, a small intervening space, having awidth of the order of some millimeters, i left between the valves 2 and2a, that at combustion and top dead center are considered as closed, andthe piston dome 9 thereby permits valves 2 and 2a to be slightly liftedeven at top dead center, whereby a weak overlap is provided by them evenin such a position, without however prejudicing the compactness ofcombustion chamber.

In short, while in the conventional four stroke, high rpm. engines forracing pur oses, very compact combustion chambers, very large valves andvery short strokes have been attained by having the whole swept volumesplit-up into a very large number of cylinders, the very same, orgreater, advantages can be obtained by the invention by means of aspecial timing diagram, in combination with a special shape of piston,and with a very small value of the stroke/ bore ratio.

Thus, it is apparent that the structure of the invention provides, in afour stroke, high rpm. internal combustion engine which operates withspark ignition, a cylinder which has a cylinder head provided with aninner surface of predetermined configuration and a piston which isslidable within this cylinder and which has a dome provided with anupper surface which in part conforms to the configuration of the innersurface of the cylinder head and which at top dead center has this partof the upper surface of the dome located closely adjacent to the innersurface of predetermined configuration of the cylinder head so as toprovide squish. The piston and cylinder of course have a common axis andthe piston dome and cylinder head define between themselves thecombustion chamber whose cross sectional area, in a plane perpendicularto the common axis of the cylinder and piston, is substantially smallerthan the cross sectional area of the cylinder, the combustible gasesbeing displaced into the combustion chamber as a result of the squish asthe piston approaches top dead center. In accordance with the invention,the engine includes the above-described valve means which is carried bythe cylinder head and which communicates with the space between thecylinder head and piston dome for providing for flow of gases into andout of this latter space and for providing overlap of intake and exhaustboth before and after the top dead center position of the piston at theend of the exhaust stroke thereof. This valve means of the invention isof course located at least in part directly next to the part of theupper surface of the piston dome which is located directly next to theinner surface of the cylinder head when the piston is at top deadcenter, and the valve means provides for this latter part thereof aposition which is substantially closed at the instant when the piston isat top dead center so as to prevent collision between this part of thevalve means and the piston dome. Moreover, in accordance with thepresent invention, the valve means coacts with the cylinder head forproviding for the path of gas flow into and out of the latter a crosssectional area large enough to compensate for the substantially closedposition of that part of the valve means which at the instant of topdead center of the piston is located directly next to the latter. As hasbeen indicated above, this large cross sectional area for the path ofgas flow into and'out of the cylinder head,

so as to compensate for the closed or substantially closed positions ofthe valves 2 and 2a at the instant when the piston is at top deadcenter, is achieved by a number of different features of the inventionwhich may be used either separately or in combination to achieve theresults of the invention. Thus, the valves 2 and 2a in and of themselvesare of such a large size that they are far greater than normal valvesand as a result of their large size pro vide for the large crosssectional area of the gas flow to compensate for the closing orsubstantial closing'of these valves at the instant of top dead center ofthe piston. In fact, as has been indicated above, the heads of thevalves 2 and 2a are so large that they are in fact larger than thecombustion chamber 5, as is apparent from FIG. 1. One of the factorswhich contributes to the possibility of providing the large valve headsfor the valves 2 and 2a is the inclination of these valves, indicated inFIG. 2, the inner surface of the cylinder head having at the region ofthese valves an inverted V-shaped configuration while the piston domehas at the region of the valves 2 and 2a an upper surface of matchinginverted V-shaped configuration, as is also apparent from FIG. 2, sothat as a result of this V-shaped configuration there is :an increase inthe area of the inner surface of the cylinder head which provides asufficiently large area to accommodate the very large valve heads of thevalves 2 and 2a. Of course, a further feature of the present inventionwhich provides for the path of gas flow a cross sectional area largeenough to compensate for the closing or substantial closing of thevalves 2 and 2a at the instant of top dead center of the piston is theprovision of the additional valve 4 and 4a which communicate only withthe combustion chamber so as to be clear of the piston head at top deadcenter and so as to be capable of providing a continuous uninterruptedoverlap in the intake and exhaust through the movement of the pistonthrough the top dead center position thereof at the end of the exhauststroke. A further feature contributing to the compensation for theclosing or substantial closing of the valves 2 and 20! at the instant oftop dead center is the extremely small stroke-tobore ratio of the engineof the invention, this extremely small ratio, which has also beenreferred to above, resulting from the fact that the piston stroke issubstantially smaller than the diameter of the cylinder bore.

Obviously, the number of valves, the sizes and location thereof, theadditional openings of same valves, and the opening and closing timesthereof, may be selected at will, according to the particularrequirements: of each application.

Also the shape and arrangement of cylinder head and piston dome may bemodified according to the advice of designer, and is intended thereforeto cover all such changes and modifications in the appended claims.

What I claim is:

1. In a four stroke, high r.p.m. internal combustion engine whichoperates with spark ignition, a cylinder having a cylinder head providedwith an inner surface of pre. determined configurtaion, a pistonslidable in said cylinder and having a dome provided with an uppersurface which in part conforms to said configuration of said innersurface of said cylinder head and which at top dead center has said partof said upper surface located closely adjacent to said inner surface ofpredetermined configuration of said cylinder head to provide squish,said piston and cylinder having a common axis and said piston dome andcylinder head defining between themselves a combus tion chamber whosecross sectional area, in a plane perpendicular to the common axis ofsaid cylinder and piston, is substantially smaller than the crOsssectional area of said cylinder and into which combustible gases aredisplaced as a result of said squish as said piston approaches top deadcenter, and valve means carried by said cylinder head and communicatingwith the space between said cylinder head and piston dome for providingfor How of gases into and out of said space and for providing overlap ofintake and exhaust both before and after the top dead center position ofsaid piston at the end of the exhaust stroke thereof, said valve meansbeing located at least in part directly next to said part of said uppersurface of said piston dome when said piston is at top dead center andsaid valve means providing for said part thereof a position which issubstantially closed at the instant when said piston is at top deadcenter so as to prevent collision between said part of said valve meansand said piston dome, said valve means coacting with said cylinder headfor providing for the path of gas flow into and out of the latter across sectional area large enough to compensate for the substantiallyclosed position of said part of said valve means at said instant of topdead center of said piston.

2. The combination of claim 1 and wherein said piston has a stroke whichis substantally smaller than the diameter of said cylinder.

3. The combination of claim 1 and wherein said valve means includes atleast an intake valve and an exhaust valve located directly next to saidpart of said upper surface of said piston dome when said piston is attop dead center and having substantially closed positions at the instantof top dead center, said intake and exhaust valves respectively havingvalve heads large enough to provide for said large cross sectional areaof the path of gas flow which compensates for the substantially closedpositions of said valves at the instant of top dead center of saidpiston.

4. The combination of claim 3 and wherein said valve heads are largerthan said combustion chamber.

5. The combination of claim 3 and wherein said valves respectively haveaxes which are inclined with respect to the common axis of said pistonand cylinder, said part of said upper surface of said piston dome havingan inverted, substantially V-shaped configuration and said inner surfaceof said cylinder head having a matching inverted, substantially V-shapedconfiguration at least at the region of said inner surface of saidcylinder head which is located closely adjacent to said piston dome whensaid piston is at top dead center, said valve heads being situated atsaid surface of said cylinder head which is of inverted, substantiallyV-shaped configuration.

6. The combination of claim 1 and wherein said valve means includes atleast one valve situated at and communicating with said combustionchamber and having an open position clear of said piston when the latteris at top dead center at the end of the exhaust stroke.

'7. The combination of claim 6 and wherein said one valve is an intakevalve.

8. The combination of claim 6 and wherein said one valve is an exhaustvalve.

9. The combination of claim 1 and wherein said valve means includes anintake and an exhaust valve situated at and communicating with saidcombustion chamber and both having open positions clear of said pistonat the top dead center position of the latter at the end of the exhauststroke.

10. The combination of claim 9 and wherein said part of said valve meansis formed by an additional pair of intake and exhaust valves situateddirectly next to said upper surface of said part of said piston domewhen said piston is at top dead center and having substantially closedpositions at the instant of top dead center for preventing collisionbetween said piston and said additional pair of valves, said pair ofadditional valves both having open positions before and after the topdead center position of said piston at the end of the exhaust strokethereof.

11. The combination of claim 10 and wherein said combustion chamber isoffset with respect to and situated to one side of said common axis ofsaid cylinder and piston.

References Cited UNITED STATES PATENTS 2,011,992 8/1935 Aseltine 123-752,235,710 3/1941 Hoffman 123-75 2,362,622 11/1944 Fischer 123-1932,428,886 10/1947 MacPherson 123l9l 2,644,436 7/1953 Berlyn 123-902,647,500 8/1953 Lang 123-90 MARK NEWMAN, Primary Examiner.

WENDELL E. BURNS, Examiner.

1. IN A FOUR STROKE, HIGH R.P.M. INTERNAL COMBUSTION ENGINE WHICHOPERATES WITH SPARK IGNITION, A CYLINDER HAVING A CYLINDER HEAD PROVIDEDWITH AN INNER SURFACE OF PREDETERMINED CONFIGURATION, A PISTON SLIDABLEIN SAID CYLINDER AND HAVING A DOME PROVIDED WITH AN UPPER SURFACE WHICHIN PART CONFORMS TO SAID CONFIGURATION OF SAID INNER SURFACE OF SAIDCYLINDER HEAD AND WHICH AT TOP DEAD CENTER HAS SAID PART OF SAID UPPERSURFACE LOCATED CLOSELY ADJACENT TO SAID INNER SURFACE OF PREDETERMINEDCONFIGURATION OF SAID CYLINDER HEAD TO PROVIDE SQUISH, SAID PISTON ANDCYLINDER HAVING A COMMON AXIS AND SAID PISTON DOME AND CYLINDER HEADDEFINING BETWEEN THEMSELVES A COMBUSTION CHAMBER WHOSE CROSS SECTIONALAREA, IN A PLANE PERPENDICULAR TO THE COMMON AXIS OF SAID CYLINDER ANDPISTON, IS SUBSTANTIALLY SMALLER THAN THE CROSS SECTIONAL AREA OF SAIDCYLINDER AND INTO WHICH COMBUSTIBLE GASES ARE DISPLACED AS A RESULT OFSAID SQUISH AS SAID PISTON APPROACHES TOP DEAD CENTER, AND VALVE MEANSCARRIED BY SAID CYLINDER HEAD AND COMMUNICATING WITH THE SPACE BETWEENSAID CYLINDER HEAD AND PISTON DOME FOR PROVIDING FOR FLOW OF GASES INTOAND OUT OF SAID SPACE AND FOR PROVIDING OVERLAP OF INTAKE AND EXHAUSTBOTH BEFORE AND AFTER THE TOP DEAD CENTER POSITION OF SAID PISTON AT THEEND OF THE EXHAUST STROKE THEREOF, SAID VALVE MEANS BEING LOCATED ATLEAST IN PART DIRECTLY NEXT TO SAID PART OF SAID UPPER SURFACE OF SAIDPISTON DOME WHEN SAID PISTON IS AT TOP DEAD CENTER AND SAID VALVE MEANSPROVIDING FOR SAID PART THEREOF A POSITION WHICH IS SUBSTANTIALLY CLOSEDAT THE INSTANT WHEN SAID PISTON IS AT TOP DEAD CENTER SO AS TO PREVENTCOLLISION BETWEEN SAID PART OF SAID VALVE MEANS AND SAID PISTON DOME,SAID VALVE MEANS COACTING WITH SAID CYLINDER HEAD FOR PROVIDING FOR THEPATH OF GAS FLOW INTO AND OUT OF THE LATTER A CROSS SECTIONAL AREA LARGEENOUGH TO COMPENSATE FOR THE SUBSTANTIALLY CLOSED POSITION OF SAID PARTOF SAID VALVE MEANS AT SAID INSTANT OF TOP DEAD CENTER OF SAID PISTON.